The disclosures of Japanese Patent Application Nos. HEI 11-236280 filed on Aug. 24, 1999, HEI 11-236305 filed on Aug. 24, 1999, HEI 11-236327 filed on Aug. 24, 1999, HEI 11-236356 filed on Aug. 24, 1999 and HEI 251062 filed on Sep. 6, 1999 including the specification, drawings and abstract are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a method for manufacturing a sound-proof product, and more particularly to a method for manufacturing a sound-proof product in which a processed material as a mixture of chip-like solid matters made of a lightweight material and a thermoplastic fibrous binder is injected with the air into a mold so as to fill the mold, and the sound-proof product is molded or shaped by hot press. This invention is also concerned with a sound-proof product manufactured by the above method.
2. Description of the Related Art
The present invention is particularly preferably applicable to sound-proof products using non-metallic shredder residue composed of, for example, wastes of vehicles, as a recycled material, and also preferably applicable to sound-proof products, such as dash silencers or floor silencers, for use in vehicles.
As a prevailing technique for manufacturing sound-proof products, such as dash silencers or floor silencers for vehicles, having a reduced volume density and excellent sound-proof and vibration damping/isolating capabilities, chip-like solid matters made of a lightweight material and a thermoplastic fibrous binder are mixed with each other, and introduced into a mold of hot press type in which press molding of a sound-proof product is performed.
In this case, it is particularly economical and meaningful in terms of recycling to effectively use non-metallic shredder residue extracted from, for example, wastes of vehicles, as chip-like solid matters of a lightweight material.
In the technology of manufacturing sound-proof products, typical methods of introducing the above mixture (processed material) into a mold include a method as disclosed in Japanese Laid-open Patent Publication No. 8-112584 in which the processed material is deposited in the form of a sheet, and brought into a cavity between the upper and lower sections of the mold, and a method in which the processed material is injected with the air into a mold so as to fill the mold. The latter method is considered as more useful in view of a higher manufacturing efficiency.
For example, a sound-proof product, such as a dash silencer or a floor silencer for vehicles, generally takes the form of a thin plate, which is also formed with many bent portions. Accordingly, the cavity of a mold used for forming the sound-proof product is also shaped like a thin plate having a cross section including many bent portions or corners. The processed material to be injected into the mold, on the other hand, consists principally of non-metallic shredder residue such as soft urethane foam, a fibrous binder, and so forth, and is thus likely to deform under compression.
Upon injection of the processed material into the mold, therefore, numerous air holes or blowholes appear in the cavity of the mold, and the processed material is particularly likely to be caught by and accumulated at bent portions in cross section, thus causing the problems as follows.
(1) Since the entire cavity needs to be filled with the processed material against the above-described accumulation phenomenon, it takes a relatively long time to inject the processed material into the cavity, resulting in an increased molding cycle time.
(2) The processed material is more likely to be accumulated in some parts of the cavity, and less likely to be accumulated in other parts of the cavity, resulting in reduced uniformity in the filling density of the processed material. Consequently, defectives are likely to be produced which suffer from ununiformity in the strength of the sound-proof product and sound-proof characteristics as measured at different portions of the member after molding.
(3) Since the above problems (1), (2) are caused by the thin, wide shape of the cavity with many bent portions in cross section, the sound-proof product, in particular, a small-thickness portion thereof, must be designed with a considerably reduced degree of freedom, so as to avoid these problems as far as possible.
The present invention aims at solving the above-described problems in a method for manufacturing sound-proof products, wherein a processed material comprising a mixture of chip-like solid matters of a lightweight material and a fibrous binder is injected with the air into a mold so as to fill the mold, and the sound-proof product is molded by hot press. The hot press is to press a heated material by a heated apparatus, to press a heated material by an apparatus which is not heated, or to press a material which is not heated by a heated apparatus and so on.
The present invention has been developed in the light of the above-described situations. It is therefore an object of the present invention to provide a method for manufacturing a sound-proof product wherein a processed material is injected into a preform mold without causing air holes or blowholes to appear in the cavity, and without causing accumulation of the processed material at bent portions of the cavity in cross section. It is also an object of the invention to provide a sound-proof product manufactured by the above method.
To accomplish the above object, the present invention provides a method for manufacturing a sound-proof product, in which a processed material as a mixture of chip-like solid matters made of a lightweight material and a thermoplastic fibrous binder is injected with the air into a preform mold having a molding surface that is designed for preliminary molding prior to main molding, to effect preform molding, and a preformed mass formed by the preform molding is fed to a main mold having a molding surface corresponding to the shape of the sound-proof product, and subjected to main molding by hot press, to provide the sound-proof product.
The cavity of the preform mold with a molding surface having a simpler shape (e.g., a flat shape or generally flat shape) than that of the main mold may be shaped in the form of a thin plate, but does not include bent portions in cross section thereof. When the processed material is injected into the preform mold so as to fill the mold, therefore, air holes are not generated in the cavity, and the processed material is not accumulated at bent portions of the cavity in cross section.
Consequently, the process of injecting the processed material can be quickly and smoothly implemented, with a result of reduced molding cycle time, which is advantageous in view of the problem (1) as described above. With regard to the problem (2), there is no local portion(s) in the cavity at which the processed material is particularly likely to be accumulated, and therefore the filling density of the processed material is made uniform. It is thus possible to produce a sound-proof product having uniform strength and sound-proof characteristics in respective portions thereof. With regard to the problem (3), the sound-proof product, in particular, its portion(s) to be formed with a small thickness, can be designed with an increased degree of freedom.
In one preferred form of the invention, an opened and disintegrated material is formed by holding a material in which the chip-like solid matters made of a lightweight material are bound by the fibrous binder, in a compressed state, and at the same time scraping a small amount of the material at a time, and an opened and crushed material may be formed by crushing the opened and disintegrated material. The opened and crushed material is then put into a sound-proof product manufacturing line having a molding process, as the chip-like solid matters.
In another preferred form of the invention, the processed material is formed by holding a laminated structure including upper and lower layers comprising the chip-like solid matters and an intermediate layer comprising the fibrous binder, in a compressed state, and at the same time scraping a small amount of the laminated structure at a time.
In a further preferred form of the invention, the processed material is injected with the air into the preform mold to fill the preform mold, and the amount of the air blowing into the mold is reduced with an increase in blowing resistance as the preform mold is filled with the processed material.
In a still further preferred form of the invention, the processed material and the mold are heated in the molding process, and subsequently cooled so as to allow the formed article to be taken out of the mold, by passing hot air and cold air, respectively, through vent holes that are open to molding surfaces of upper and lower sections of the mold.
The present invention also provides a sound-proof product manufactured by the above manufacturing method.